The present disclosure relates to a charging device having a charging roller configured to charge a surface of an image carrier, a drum unit and an image forming apparatus which are provided with the charging device.
In an image forming apparatus using an electrophotographic process, a charging device of a contact charging type is broadly put into practical use, in which a charging roller made of conductive material comes into contact with a surface of a photosensitive drum (an image carrier) and then voltage is applied between the photosensitive drum and the charging roller to charge the surface of the photosensitive drum.
The charging device of the contact charging type has sometimes a configuration that both end portion of the charging roller are supported by bearings in a rotatable manner and the bearings are biased toward the photosensitive drum by a pressing spring so as to bring the charging roller come into contact with the photosensitive drum. If the charging roller is displaced, a charged potential of the photosensitive drum is not uniform and an image failure may occur. Accordingly, the bearings are required to be positioned with a high precision.
Then, the charging device has a configuration that a pair of guide walls is formed in a casing and the bearings are guided between the guide walls. In such a configuration, because the guide walls have not sufficient strength and are easily deformed, the charging roller may be displaced. If the charging roller is displaced, the charged potential of the photosensitive drum is not uniform and an image failure may occur as described above.